Marilyn T. Marron

Tumor-derived CD4+CD25+ regulatory T cell suppression of dendritic cell function involves TGF-β and IL-10

CD4+CD25+ regulatory T cells have been characterized as a critical population of immunosuppressive cells. They play a crucial role in cancer progression by inhibiting the effector function of CD4+ or CD8+ T lymphocytes. However, whether regulatory T lymphocytes that expand during tumor progression can modulate dendritic cell function is unclear. To address this issue, we have evaluated the inhibitory potential of CD4+CD25+ regulatory T cells from mice bearing a BCR–ABL+ leukemia on bone marrow-derived dendritic cells. We present data demonstrating that CD4+CD25+FoxP3+ regulatory T cells from tumor-bearing animals impede dendritic cell function by down-regulating the activation of the transcription factor NF-κB. The expression of the co-stimulatory molecules CD80, CD86 and CD40, the production of TNF-α, IL-12, and CCL5/RANTES by the suppressed DC is strongly down-regulated. The suppression mechanism requires TGF-β and IL-10 and is associated with induction of the Smad signaling pathway and activation of the STAT3 transcription factor.

Hsp90 inhibitors deplete key anti-apoptotic proteins in pediatric solid tumor cells and demonstrate synergistic anticancer activity with cisplatin

Drugs that inhibit the function of heat shock protein 90 (Hsp90) are of interest in the treatment of pediatric cancers because these agents deplete the cellular levels of signaling molecules that are important for the growth and survival of many childhood tumors. To generate preclinical data in anticipation of clinical trials of Hsp90 inhibitors in children, we evaluated the effects of the Hsp90 inhibitor geldanamycin (GA) alone and in combination with cis‐platinum (II)‐diamine dichloride (cisplatin) in pediatric tumor cells. Immunoblotting demonstrated depletion of the Hsp90 client proteins AKT and the type 1 insulin‐like growth factor receptor (IGF1R) in a panel of pediatric tumor cell lines after exposure to GA. Drug exposure also led to a dramatic decrease in cell survival/proliferation in MYCN‐amplified and non‐amplified neuroblastoma cells. Moderate inhibition of survival/proliferation was observed in RB‐deficient and wild‐type osteosarcoma cells. Treatment of neuroblastoma and osteosarcoma cell lines with GA in combination with cisplatin resulted in greater than additive inhibition of survival/proliferation based on median dose analysis. Exposure to this drug combination also resulted in a marked increase in nuclear fragmentation as assessed by terminal deoxynucleotide transferase‐mediated UTP nick end labeling (TUNEL) analysis. Combined exposure also abrogated the ability of GA to induce a cytoprotective heat shock response and resulted in Hsp90 adduct formation. Our findings suggest that Hsp90 inhibitors may prove useful either alone or as a component of multi‐drug regimens in the treatment of neuroblastoma and osteosarcoma.

Efficient purification of the biosurfactant viscosin from Pseudomonas libanensis strain M9-3 and its physicochemical and biological properties.

Viscosin (1), an effective surface-active cyclic lipopeptide, was efficiently recovered from Pseudomonas libanensis M9-3 with a simple purification protocol. A major pigment also obtained during this process was identified as phenazine-1-carboxylic acid. The critical micelle concentration (cmc) of viscosin was determined to be 54 mg L (-1), and the minimum surface tension between air and water at the cmc was 28 mN m (-1). Viscosin forms stable emulsions even at low concentrations (7.5 mg L (-1)), and the conditional stability constant for a cadmium-viscosin complex was determined to be 5.87. The physicochemical properties measured for viscosin are similar to other well-studied biosurfactants such as rhamnolipid and surfactin. Viscosin inhibited migration of the metastatic prostate cancer cell line, PC-3M, without visible toxicity. These properties suggest the potential of viscosin in environmental and biomedical applications.

2,3-Dihydrowithaferin A-3β-O-sulfate, a new potential prodrug of withaferin A from aeroponically grown Withania somnifera

Preparations of the roots of the medicinal plant Withania somnifera (L.) Dunal commonly called ashwagandha have been used for millennia in the Ayurvedic medical tradition of India as a general tonic to relieve stress and enhance health, especially in the elderly. In modern times, ashwagandha has been shown to possess intriguing antiangiogenic and anticancer activity, largely attributable to the presence of the steroidal lactone withaferin A as the major constituent. When cultured using the aeroponic technique, however, this plant was found to produce a new natural product, 2,3-dihydrowithaferin A-3beta-O-sulfate (1), as the predominant constituent of methanolic extracts prepared from aerial tissues. The characteristic bioactivities exhibited by 1 including inhibition of cancer cell proliferation/survival, disruption of cytoskeletal organization and induction of the cellular heat-shock response paralleled those displayed by withaferin A (2). The delayed onset of action and reduced potency of 1 in cell culture along with previous observations demonstrating the requirement of the 2(3)-double bond in withanolides for bioactivity suggested that 1 might be converted to 2 in cell culture media and this was confirmed by HPLC analysis. The abundant yield of 1 from aeroponically cultivated plants, its good aqueous solubility and spontaneous conversion to 2 under cell culture conditions, suggest that 1 could prove useful as a readily formulated prodrug of withaferin A that merits further evaluation in animal models.

Structure–Activity Relationships for Withanolides as Inducers of the Cellular Heat-Shock Response

To understand the relationship between the structure and the remarkably diverse bioactivities reported for withanolides, we obtained withaferin A (WA; 1) and 36 analogues (2-37) and compared their cytotoxicity to cytoprotective heat-shock-inducing activity (HSA). By analyzing structure-activity relationships for the series, we found that the ring A enone is essential for both bioactivities. Acetylation of 27-OH of 4-epi-WA (28) to 33 enhanced both activities, whereas introduction of β-OH to WA at C-12 (29) and C-15 (30) decreased both activities. Introduction of β-OAc to 4,27-diacetyl-WA (16) at C-15 (37) decreased HSA without affecting cytotoxicity, but at C-12 (36), it had minimal effect. Importantly, acetylation of 27-OH, yielding 15 from 1, 16 from 14, and 35 from 34, enhanced HSA without increasing cytotoxicity. Our findings demonstrate that the withanolide scaffold can be modified to enhance HSA selectively, thereby assisting development of natural product-inspired drugs to combat protein aggregation-associated diseases by stimulating cellular defense mechanisms.

Natural killer cells play a key role in the antitumor immunity generated by chaperone-rich cell lysate vaccination

Tumor derived chaperone‐rich cell lysate (CRCL) when isolated from tumor tissues is a potent vaccine that contains at least 4 of the highly immunogenic heat shock proteins (HSP) such as HSP70, HSP90, glucose related protein 94 and calreticulin. We have previously documented that CRCL provides both a source of tumor antigens and danger signals triggering dendritic cell (DC) activation. Immunization with tumor derived CRCL elicits tumor‐specific T cell responses leading to tumor regression. In the current study, we further dissect the mechanisms by which CRCL simulates the immune system, and demonstrate that natural killer (NK) cells are required for effective antitumor effects to take place. Our results illustrate that CRCL directly stimulates proinflammatory cytokine and chemokine production by NK cells, which may lead to activation and recruitment of macrophages at the tumor site. Thus, this report provides further insight into the function of CRCL as an immunostimulant against cancer.

A phase I clinical trial of bavituximab and paclitaxel in patients with HER2 negative metastatic breast cancer

Bavituximab is a chimeric monoclonal antibody that targets phosphatidylserine (PS). PS is externalized on cells in the tumor microenvironment when exposed to hypoxia and/or other physiological stressors. On attaching to PS, bavituximab is thought to promote antitumor immunity through its effects on PS receptors in monocytes, and myeloid‐derived suppressor cells, as well as trigger antitumor effects by inducing an antibody‐dependent cellular cytotoxicity on tumor‐associated endothelial cells. We conducted a phase I clinical trial of bavituximab in combination with paclitaxel in patients with HER2‐negative metastatic breast cancer. Patients were treated with weekly paclitaxel (80 mg/m2 for 3/4 weeks) and weekly bavituximab (3 mg/kg for 4/4 weeks). Correlative studies included the measurement of circulating microparticles, endothelial cells, and apoptotic tumor cells by flow cytometry. Fourteen patients with metastatic breast cancer were enrolled; all were evaluable for toxicity and 13 were evaluable for response. Treatment resulted in an overall response rate (RR) of 85% with a median progression‐free survival (PFS) of 7.3 months. Bone pain, fatigue, headache, and neutropenia were the most common adverse effects. Infusion‐related reactions were the most common adverse event related to bavituximab therapy. Correlative studies showed an increase in the PS‐expressing apoptotic circulating tumor cells in response to bavituximab, but not with paclitaxel. No changes in the number of circulating endothelial cells or apoptotic endothelial cells were observed with therapy. Platelet and monocyte‐derived microparticles decreased after initiation of bavituximab. Bavituximab in combination with paclitaxel is well tolerated for treatment of patients with metastatic breast cancer with promising results observed in terms of clinical RRs and PFS. The toxicity profile of bavituximab is notable for manageable infusion‐related reactions with no evidence for increased thrombogenicity. Recent preclinical data suggest that bavituximab can also promote antitumor immune activity that should be explored in future clinical trials.

Chaperone-rich cell lysate embedded with BCR-ABL peptide demonstrates enhanced anti-tumor activity against a murine BCR-ABL positive leukemia

Chaperone proteins are effective antitumor vaccines when purified from a tumor source, some of which are in clinical trials. Such vaccines culminate in tumor‐specific T cell responses, implicating the role of adaptive immunity. We have developed a rapid and efficient procedure utilizing an isoelectric focusing technique to obtain vaccines from tumor or normal tissues called chaperone‐rich cell lysate (CRCL). Tumor‐associated peptides the currency of T cell‐mediated anticancer immunity are believed to be purveyed by chaperone vaccines. Our purpose was to demonstrate our ability to manipulate the peptide antigen repertoire of CRCL vaccines as a novel anticancer strategy. Our methods allow us to prepare “designer” CRCL utilizing the immunostimulation activity and the carrying capacity of CRCL to quantitatively acquire and deliver exogenous antigenic peptides (e.g., derived from the oncogenic BCR/ABL protein in chronic myelogenous leukemia). Using fluorescence‐based and antigen‐presentation assays we determined that significant quantities of exogenously added peptide could accumulate in “designer” CRCL and could stimulate T cell activation. Further, we concluded that peptide‐embedded CRCL devoid of other antigens could generate potent immunity against pre‐established mu‐rine leukemia. Designer CRCL allows for the development of personalized vaccines against cancers expressing known antigens by embedding antigens into CRCL derived from normal tissue.–Kislin, K. L., Marron, M. T., Li, G. Graner M. W. Katsanis E. Chaperone‐rich cell lysate embedded with BCR‐ABL peptide demonstrates enhanced anti‐tumor activity against a murine BCR‐ABL positive leukemia FASEB J. 21, 2173–2184 (2007)

Synthesis and biological evaluation of novobiocin analogues as potential heat shock protein 90 inhibitors.

Recent studies have shown that novobiocin (NB), a member of the coumermycin (CA) family of antibiotics with demonstrated DNA gyrase inhibitory activity, inhibits Heat shock protein 90 (HSP90) by binding weakly to a putative ATP-binding site within its C-terminus. To develop more potent HSP90 inhibitors that target this site and to define structure-activity relationships (SARs) for this class of compounds, we have synthesized twenty seven 3-amido-7-noviosylcoumarin analogues starting from NB and CA. These were evaluated for evidence of HSP90 inhibition using several biological assays including inhibition of cell proliferation and cell cycle arrest, induction of the heat shock response, inhibition of luciferase-refolding in vitro, and depletion of the HSP90 client protein c-erbB-2/HER-2/neu (HER2). This SAR study revealed that a substantial increase in biological activity can be achieved by introduction of an indole-2-carboxamide group in place of 4-hydroxy-isopentylbenzamido group at C-3 of NB in addition to removal/derivatization of the 4-hydroxyl group from the coumarin ring. Methylation of the 4-hydroxyl group in the coumarin moiety moderately increased biological activity as shown by compounds 11 and 13. Our most potent new analogue 19 demonstrated biological activities consistent with known HSP90-binding agents, but with greater potency than NB.

An analog of withaferin a activates the MAPK and glutathione "stress" pathways and inhibits pancreatic cancer cell proliferation

Withaferin A (WA) (1) and two analogs [4-epi-withaferin A (2) and 4,27-diacetyl-4-epi-withaferin A (3)] were evaluated for antitumor activity in pancreatic cancer cells. IC50 for 1, 2, and 3 were 0.87, 0.45, and 0.29 μM (BxPC-3); 1.28, 1.53, and 0.52 μM (MIAPaCa-2); and 0.59, 2.25, and 0.56 μM (PANC-1), respectively. We chose WA analog 3 for functional studies with confirmatory RT-PCR and Western blotting. ANOVA identified 33 (MIAPaCa-2), 54 (PANC-1), and 48 (BxPC-3) gene expression changes. Fisher exact test demonstrated MAPK and glutathione pathways to be overexpressed with WA analog 3. WA analog 3 elicits a dose- and time-dependent apoptosis, activates MAPK and glutathione “stress” pathways, and inhibits proliferation.